In general, dynamoelectric machines, such as electric motors, are basically categorized as being of three different types of construction, i.e., a totally enclosed motor, a drip-proof motor and an open motor. One definition of a totally enclosed motor is that it is so enclosed as to prevent the free exchange of air between the inside and the outside of the motor housing but not sufficiently enclosed to be air tight, and an example of such totally enclosed motor is illustrated in U.S. Pat. No. 2,974,856 issued to R. E. Seely on Mar. 14, 1961. A definition of an open motor is that it has ventilating openings which permit passage of external cooling air over and around the windings of such open motor, and examples of such open motor are illustrated in U.S. Pat. No. 3,164,422 issued Jan. 5, 1965 to Paul B. Shaffer et al. and U.S. Pat. No. 3,858,067 issued Dec. 31, 1974 to Charles W. Otto. One definition of a drip-proof motor is that it is an open motor in which the ventilation openings are so constructed that successful operation is not interfered with when drops of liquid or solid particles strike or enter the housing thereof at any angle from about 0.degree. to about 15.degree. downwardly from the vertical, and an example of such drip-proof motor is illustrated in U.S. Pat. No. 3,270,223 issued Aug. 30, 1966 to R. E. Seely. The foregoing definitions of totally enclosed, drip proof and open motors may be found in the C. G. Veinott textbook entitled "Fractional and Subfractional Horsepower Electric Motors" (third edition, McGraw-Hill Book Co.).
Further, with respect to the open motor construction of the aforementioned U.S. Pat. No. 3,858,067, a plurality of beams secured to a stator had a pair of opposite end portions received within a plurality of sockets provided in a pair of opposite end frames, respectively. In order to secure the opposite end frames against displacement from the opposite end portions of the beams, metallic plugs were solidified and contained generally within the sockets and were respectively interconnected between the opposite end portions of the beams and at least a portion of the sockets.
In U.S. Pat. No. 3,164,422, the open motor construction shown therein included a stator having four circumferentially spaced apart welding surfaces on the periphery thereof, and a pair of opposite end frames were positioned adjacent opposite sides or faces of the stator, respectively. Four spaced apart flanges integrally formed on the opposite end frames extended axially therefrom so as to be arranged generally in aligned relation with each other and in overlaying relation with the four peripheral welding surfaces on the stator, respectively. In order to secure the stator and opposite end frames together against displacement, the four flanges of the opposite end frames were spot welded to the four peripheral welding surfaces on the stator, respectively.
The aforementioned White U.S. Pat. No. 4,473,764 and the White and Kuzan U.S. Pat. No. 486,378 illustrate another open motor construction and method of assembling such. In these applications, an end frame has a pair of opposite faces with a set of apertures intersecting therebetween. A set of beams secured to a stator each have an abutment end disposed at least adjacent one of the opposite faces of the end frame, and the tabs of the beams protrude through the apertures in the end frame in spaced apart relation with the sidewalls of the apertures, respectively. The tabs are welded into displacement preventing engagement with the other opposite face of the end frame at least adjacent the apertures therein, respectively.
While the above discussed prior art dynamoelectric machines and methods of assembling such undoubtedly exhibit salient features, it is quite desirable to provide an improved yet inexpensive dynamoelectric machine having the capability to be used for a number of diverse applications having different duty capacities which may require different structural strengths with little change in the structural components and with little change in the method of assembling such.